PROJECT SUMMARY There are eight human herpesviruses, large DNA viruses that each infect over 60% of the population and cause a large number of complications that are major public health concerns. Each human herpesvirus infects via a primary site, enters a latent state in a secondary tissue, and then reactivates before spread back to the primary site and transmission to a secondary host. A humoral immune response is generated during the primary infection, generating antibodies that can target and neutralize extracellular virions. Therefore, each herpesvirus must reactivate and spread in the face of a neutralizing antibody response. The most effective way to avoid the antibody response is for the virus to spread from an infected cell to a neighboring uninfected cell directly, without an extracellular stage. In this proposal we will examine the role of a host protein, Protein- tyrosine phosphatase 1B (PTP1B), in mediating the spread of Herpes simplex virus (HSV-1) between tissues in an animal model. HSV-1 infects epithelia, but the secondary neuroinvasive nature of the virus can lead to complications, including herpes keratitis, Mollaret?s meningitis and herpes encephalitis. A number of studies have examined the role of viral proteins in mediating cell-to-cell spread of HSV-1 in vivo, but our studies will focus on the role of host proteins. Our preliminary data strongly support a role for PTP1B, a signaling molecule known to play a role in the formation of cell junctions, in cell-to-cell spread of HSV-1 in vitro. We will use the Zosteriform model of HSV-1 infection in mice, which allows quantification of the primary infection, spread through the nervous system, and infection at a tertiary epithelial site. We will examine the role of PTP1B on primary, secondary and tertiary HSV-1 infection in the presence or absence of a neutralizing antibody response to the virus. Then we will expand our studies to examine the cells, and time points, at which PTP1B must be present in order to facilitate full pathogenesis of HSV-1. At the conclusion of these studies we will have identified the point at which PTP1B is required for HSV-1 spread in vivo, and will be poised to expand our studies, both to other herpesviruses, and to other cellular proteins that are involved in formation or regulation of cellular junctions that may play a role if HSV-1 cell-to-cell-spread.